This invention relates to a color picture tube provided with a shadow mask, and more specifically, to a structure wherein a frame holding a shadow mask is attached to the panel of a color picture tube.
A conventional shadow mask color picture tube is disclosed in, for example, Japanese Patent Kokai Publication 216137/1987 (S62-216137). This color picture tube comprises stud pins at four corners of a skirt, a frame that holds a shadow mask, and elastic supporters that support the frame elastically on the stud pins of the skirt. This picture tube further comprises other stud pins on the upper and lower inner walls of the skirt, and other elastic supporters that elastically support the upper and lower long sides of the frame on these other stud pins. Hence, not only are the four corners of the frame supported by elastic supporters, but the two long sides of the frame are also supported by elastic supporters. This prevents twisting and deformation of the shadow mask due to its own weight.
However in the aforesaid conventional picture tube, as the frame is supported only by elastic supporters, the frame and shadow mask move in the direction of gravity depending on how the picture tube is positioned or oriented. Hence, if the picture tube is placed on its side (i.e. such that the long side of the panel is vertical), the shadow mask moves down in the direction of gravity (i.e. in the direction parallel to the long side of the panel). As a result, the positions of the holes in the shadow mask are displaced, the electron beams emitted by the electron gun pass through the holes in the mask do not land correctly on the phosphors or the panel, and color distortions of the displayed image occur.
This problem was even more serious when the phosphors consisted of thin stripes oriented in the direction parallel to the short side of the panel, and when the picture tube was large so that the frame and shadow mask were heavier.